WASHINGTON (AP) — A bipartisan agreement reached by House and Senate negotiators would set new safety standards for asbestos and other dangerous chemicals, including tens of thousands that have gone unregulated for decades.

A bill to be voted on as soon as next week would offer new protections for pregnant women, children, workers and others vulnerable to the effects of chemicals such as formaldehyde and styrene used in homes and businesses every day.

If enacted into law, the bill would be the first significant update to the Toxic Substances Control Act (pdf) since the law was adopted in 1976.

The bill, more than three years in the making, has won the backing of both industry officials and some of the Capitol's most liberal lawmakers, including Sens. Barbara Boxer of California and Edward Markey of Massachusetts.

The bill also has the support of conservative Republicans such as Sens. David Vitter of Louisiana and James Inhofe of Oklahoma.

"This is a political Halley's Comet" that may not be seen again for many years, said Markey, a former opponent of the bill who signed onto it in recent weeks after changes were made to ensure that states that regulate chemicals closely can continue to do so.

Markey called the bill "a special piece of legislation" that finally updates one of the major environmental laws approved during the 1970s.

The agreement announced Thursday merges bills that the House and Senate passed last year.

Negotiations had stalled in recent weeks, as lawmakers struggled over a provision that allows states to continue regulating toxic chemicals. The proposal announced Thursday declares that any state law or rule in place before April 22 would not be pre-empted by federal law. The proposal also would allow states to work on regulations while federal rules are being developed, a process that can take years.

Boxer, who had opposed earlier versions of the bill, said the proposal protects the rights of California, Massachusetts and other states that aggressively regulate chemicals "to continue their critical work to protect their citizens from harmful toxic chemicals." States that do not regulate chemicals closely would follow the federal standard.

The U.S. Chamber of Commerce said in a statement Thursday that the measure "goes a long way to providing businesses with much needed clarity and certainty by facilitating a more predictable federal regulatory program" for chemicals.

Richard Denison, a senior scientist for the Environmental Defense Fund, called the bill a "significant victory for public health," noting that it will require safety reviews for thousands of chemicals already in use and mandate greater scrutiny of new chemicals before they can be sold.

"While not perfect, this will be a dramatic improvement over current law," Denison said.

Chemicals used in everyday products such as household cleaners, clothing and furniture have been linked to serious illnesses, including cancer, infertility, diabetes and Parkinson's disease. Under current law, only a small fraction of chemicals used in these products have been reviewed for safety.

"People believe when they go to the grocery store or the hardware store (and) get a product, that that product has been tested and it's been determined to be safe. That isn't the case," said Sen. Tom Udall, D-N.M., a lead sponsor of the bill. "Today we are stepping forward and we are putting a law in place that will protect American families and protect children from chemicals."

Regulation of chemicals took on new urgency after a 2014 spill in West Virginia contaminated drinking water for 300,000 people. The chemical, crude MCHM, is one of thousands unregulated under current law.

Sen. Shelley Moore Capito, R-W.Va., said the spill "brought into my own home how the lack of knowledge of what's in your water supply can affect your health."

The legislation is named after the late Sen. Frank Lautenberg, a New Jersey Democrat who pushed for chemical reform before his death in 2013. Lautenberg's widow, Bonnie, praised the bill and said it was the most important legislation associated with her husband, including a landmark bill he sponsored to ban smoking on airplanes.

Under the agreement, if the federal government does not complete the regulatory process for a chemical within 3½ years, then states would be free to regulate that chemical.